Fail-safe when update class cannot be correctly reconstructed or loaded.

Previously, if the wrong base class name was written to the database, attempts to load update information could trigger a warning because there was no class_exists() check in the "updateBaseClass is set" branch. To fix that, I've moved the class_exists() closer to the place where the class name is actually used.

StateStore will still fail to load a stored update if the class name is invalid, but without a PHP warning this time. The invalid stored update information should be overwritten the next time PUC checks for updates.

Puc/v4p12/StateStore.php

@@ -180,11 +180,11 @@ protected function load() {
 				$updateClass = null;
 				if ( isset($state->updateBaseClass) ) {
 					$updateClass = $this->getLibPrefix() . $state->updateBaseClass;
-				} else if ( isset($state->updateClass) && class_exists($state->updateClass) ) {
+				} else if ( isset($state->updateClass) ) {
 					$updateClass = $state->updateClass;
 				}
 
-				if ( $updateClass !== null ) {
+				if ( ($updateClass !== null) && class_exists($updateClass) ) {
 					$this->update = call_user_func(array($updateClass, 'fromObject'), $state->update);
 				}
 			}